A carefully controlled study was conducted on the effect of different amounts of highway police patrol on accidents, traffic diversion and speed. Analysis of the data indicated that although there was no significant change between test and control routes in average speed or percentage over the speeds limit there was a significant reduction in the variance of speeds which was directly related to the enforcement level. However, no effects were found on diversion of accidents. The latter finding was at variance with the original report of the study and was due to the nature of the assumption about the accident distributions. In general, the results of the study indicated that the effects of enforcement may be very subtle and may influence traffic behaviour in a very indirect fashion.
Abstract